HN Unread Comments

This extension will keep track of comments you read on Hacker News and then show you which ones are new (it works on the "threads" page and on a individual item).
v1.3.0 changes so that the border on unread comments is only visible on the left, and is now 2px thick
v1.2 fixes the extension so that it now works on HN again.
v1.1 fixes some issues with detecting comments. It now uses a different way to track read comments, and should be more reliable. Leave comments if you find any bugs.
Source code is freely available on GitHub: http://github.com/janhancic/hn-unread-comments